TECHNICAL FIELD
[0001] The present invention relates to a cathode mixture, a method for producing the same,
and an all-solid-state lithium-sulfur battery.
BACKGROUND ART
[0002] Sulfur is known to possess a very high theoretical capacity of about 1672 mAh/g,
and lithium-sulfur batteries in which sulfur is used as a cathode active material
have been the subject of active studies. Lithium-sulfur batteries are roughly classified
into liquid lithium-sulfur batteries in which the electrolyte is liquid, and all-solid-state
lithium-sulfur batteries in which the electrolyte is solid.
[0003] A drawback of the liquid lithium-sulfur batteries is that lithium polysulfide generated
by the reaction of lithium ions with sulfur is dissolved into the electrolyte solution,
thereby adversely affecting the charge/discharge capacity and the life of the batteries.
[0004] In contrast, the all-solid-state lithium-sulfur batteries are free from the drawback
that lithium polysulfide is dissolved into the electrolyte solution, and are thus
suitable in maintaining the battery charge/discharge capacity and prolonging the battery
life. Moreover, for example, they are free of combustible organic solvents and thus
can ensure safety without the risk of electrolyte leakage or ignition, and they do
not require a separator. These excellent characteristics of the all-solid-state lithium-sulfur
batteries have been drawing attention. In the cathode mixture layer of the all-solid-state
lithium-sulfur batteries, a reversible reaction represented by the following formula
(1) occurs, wherein the reaction toward the right predominantly proceeds during discharge,
and the reaction toward the left predominantly proceeds during charge.
S+2Li
++2e
- ↔ Li
2S (1)
[0005] In the all-solid-state lithium-sulfur batteries, however, since the anode, the solid
electrolyte layer, and the cathode mixture layer are substantially free of solvents,
and the sulfur contained as a cathode active material in the cathode mixture layer
has electrical insulation properties, the cathode mixture layer has very low electron
conductivity and very low lithium-ion conductivity. Accordingly, disadvantageously,
the all-solid-state lithium-sulfur batteries exhibit poor reactivity in the reaction
shown in the formula (1) during charge and discharge, thereby failing to ensure a
sufficient charge/discharge capacity.
[0006] Patent Literature 1 discloses a cathode for all-solid lithium secondary batteries
which is prepared by mechanically milling a starting material mixture containing sulfur,
a carbon material having an average particle size of 100 nm or less, and an electrolyte
represented by Li
2S-P
xS
y where x and y each represent an integer that gives a stoichiometric ratio, and molding
the resulting complex. According to this literature, with the cathode for all-solid
lithium secondary batteries formed of the above molded product, the batteries have
a high charge/discharge capacity and can be charged and discharged at a high current
density.
CITATION LIST
PATENT LITERATURE
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0008] In fact, however, the cathode for all-solid lithium secondary batteries disclosed
in Patent Literature 1 can have difficulty in ensuring a sufficient charge/discharge
capacity when used at practical electric current levels even in low power applications
such as smartphones or personal computers although it has less difficulty at unpractically
low currents. For example, if a cathode made from sulfur, a conductive material, and
80Li
2S-20P
2S
5 as disclosed in the examples of Patent Literature 1 is used as a cathode of an all-solid-state
lithium-sulfur battery, such a battery may show an insufficient charge/discharge capacity
when high current flows. Thus, all-solid-state lithium-sulfur batteries including
the traditional cathode mixture layer still need improvement in their charge/discharge
capacity. In the present situation, there is a problem that the advantageous physical
properties of sulfur cannot be fully maximized to achieve an all-solid-state lithium-sulfur
battery that can withstand use at practically high currents.
[0009] The present invention aims to maximize the advantageous physical properties of sulfur
and provide a cathode mixture that can be suitably used in a cathode mixture layer
of an all-solid-state lithium-sulfur battery having excellent charge/discharge capacity.
The present invention also aims to provide an all-solid-state lithium-sulfur battery
including a cathode mixture layer containing the cathode mixture.
SOLUTION TO PROBLEM
[0010] As a result of various studies on cathode mixtures for use in all-solid-state lithium-sulfur
batteries, the present inventors obtained the following findings: elemental phosphorus
or phosphorus sulfide together with sulfur and/or its discharge product can be used
as cathode active materials in an all-solid-state lithium-sulfur battery to improve
the charge/discharge capacity, especially when high current flows. The present invention
was completed based on such findings.
[0011] The cathode mixture of the present invention is a cathode mixture for use in a cathode
mixture layer of an all-solid-state lithium-sulfur battery, the cathode mixture containing
the following components (A) to (D):
- (A) sulfur and/or its discharge product;
- (B) elemental phosphorus and/or PxSy where x and y independently represent an integer that gives a stoichiometric ratio;
- (C) an ion-conductive material; and
- (D) a conductive material.
[0012] In the cathode mixture of the present invention, the component (C) is preferably
a composite of Li, S, and P, and preferably contains P at a weight ratio of 0.15 to
0.55.
[0013] The composite of Li, S, and P is more preferably obtained by mechanically milling
at least a combination of Li
2S, S, and P, or at least a combination of Li
2S and P
xS
y where x and y independently represent an integer that gives a stoichiometric ratio.
[0014] The cathode mixture of the present invention is preferably obtained by mixing the
component (A) and the component (B) first and then mixing the resulting mixture with
the component (C) and the component (D).
[0015] In the cathode mixture of the present invention, the component (B) is preferably
present in an amount of 1 to 35% by weight of the amount of the component (A).
[0016] In the cathode mixture of the present invention, the component (D) preferably includes
a conductive component (D1) that includes a carbon material having a specific surface
area of 1000 m
2/g or more. The component (D) may further include at least one conductive component
(D2) selected from the group consisting of graphite, acetylene black, carbon nanotube,
and carbon fiber.
[0017] In the cathode mixture of the present invention, the component (A) and the component
(B) are preferably present in a combined amount of 40% by weight or more of the total
cathode mixture.
[0018] The composite of Li, S, and P may be obtained by mechanically milling the combination
of Li
2S, S, and P or the combination of Li
2S and P
xS
y, and further at least one selected from the group consisting of M
zS where M represents Si, Ge, B, or Al, and z represents an integer that gives a stoichiometric
ratio, phosphorus oxide, lithium oxide, and lithium iodide.
[0019] The all-solid-state lithium-sulfur battery of the present invention includes: a cathode
mixture layer containing the cathode mixture of the present invention; a solid electrolyte
layer; an anode; and a current collector.
[0020] The method for producing the cathode mixture of the present invention at least includes:
step (1) of mixing the component (A) and the component (B); and
step (2) of mixing a mixture obtained in the step (1) with the component (C) and the
component (D) simultaneously or separately.
ADVANTAGEOUS EFFECTS OF INVENTION
[0021] The cathode mixture of the present invention contains (B) elemental phosphorus and/or
P
xS
y in combination with (A) sulfur and/or its discharge product, (C) an ion-conductive
material, and (D) a conductive material. The component (B) serves, together with the
component (A), as a cathode active material in the cathode mixture. Then, the reactivity
of the reaction shown in the formula (1) is improved by electron donation from P of
the component (B) to S of the component (A) . As a result, if such a cathode mixture
is used in a cathode mixture layer of an all-solid-state lithium-sulfur battery, the
provided all-solid-state lithium-sulfur battery shows low resistance when sulfur,
electrons, and lithium ions react with each other at the reaction interface, and thus
has excellent charge/discharge characteristics. In particular, the present invention
is advantageous in that a high charge/discharge capacity is shown not only at a low
current (for example, about 0.5 to 1.0 mA/cm
2) but also at a high current (for example, 5 mA/cm
2 or more).
[0022] Moreover, since the all-solid-state lithium-sulfur battery of the present invention
includes a cathode mixture layer containing the cathode mixture of the present invention,
it has excellent charge/discharge characteristics.
[0023] Moreover, since the method for producing the cathode mixture of the present invention
includes mixing the component (A) and the component (B) first and then mixing the
resulting mixture with the component (C) and the component (D), the electron donation
from P of the component (B) to S of the component (A) is more ensured for the cathode
active materials in the obtained cathode mixture. The produced cathode mixture can
provide an all-solid-state lithium-sulfur battery having excellent charge/discharge
characteristics.
[0024] The cathode mixture and the all-solid-state lithium-sulfur battery including the
cathode mixture can be used in, for example, electric cars or hybrid cars, and the
present invention therefore can contribute to reducing CO
2 emissions.
BRIEF DESCRIPTION OF DRAWINGS
[0025] Fig. 1 is a cross-sectional view schematically showing an exemplary embodiment of
the all-solid-state lithium-sulfur battery of the present invention.
DESCRIPTION OF EMBODIMENTS
«Cathode mixture»
[0026] A description is given on the cathode mixture of the present invention first.
[0027] The cathode mixture of the present invention is characterized as a cathode mixture
for use in a cathode mixture layer of an all-solid-state lithium-sulfur battery, the
cathode mixture containing the following components (A) to (D):
- (A) sulfur and/or its discharge product;
- (B) elemental phosphorus and/or PxSy where x and y independently represent an integer that gives a stoichiometric ratio;
- (C) an ion-conductive material; and
- (D) a conductive material.
<Component (A): sulfur and/or its discharge product>
[0028] The cathode mixture of the present invention contains (A) sulfur and/or its discharge
product as a cathode active material. The sulfur may be elemental sulfur. The discharge
product of sulfur is not particularly limited, and examples include lithium polysulfides
such as Li
2S
8, Li
2S
4, and Li
2S
2, and lithium sulfide (Li
2S). These compounds may be used alone or in combinations of two or more. These compounds
may also be used with elemental sulfur.
<Component (B): elemental phosphorus and/or PxSy>
[0029] The cathode mixture of the present invention contains (B) elemental phosphorus and/or
P
xS
y where x and y independently represent an integer that gives a stoichiometric ratio.
Specific examples of the P
xS
y include P
2S
3, P
2S
5, P
4S
3, and P
4S
7. The cathode mixture may contain only one type of component (B) or may contain two
or more types of components (B) in combination.
[0030] The cathode mixture of the present invention contains the above-described components
(A) and (B) as cathode active materials. Since the cathode mixture contains such specific
two types of components as cathode active materials, the reactivity of the reaction
shown in the formula (1) is improved by electron donation from P of the component
(B) to S of the component (A), as described above. As a result, if such a cathode
mixture is used in a cathode mixture layer of an all-solid-state lithium-sulfur battery,
the provided all-solid-state lithium-sulfur battery shows low resistance when sulfur,
electrons, and lithium ions react with each other at the reaction interface, and thus
has excellent charge/discharge characteristics.
[0031] The amount of the component (B) is preferably 1 to 35% by weight of the amount of
the component (A). If the amount of the component (B) relative to the component (A)
is less than 1% by weight, the effect of improving the reactivity of sulfur by phosphorus
may be insufficient, thereby failing to achieve a large discharge capacity. Conversely,
if the amount is more than 35% by weight, the amount of the component (A) in the cathode
mixture is reduced, possibly resulting in a decrease in discharge capacity.
<Component (C): ion-conductive material>
[0032] The cathode mixture of the present invention contains the ion-conductive material
(C) as a solid electrolyte. The ion-conductive material (C) is not particularly limited,
and those used in the technical field related to the present application may be used.
The ion-conductive material (C) preferably contains phosphorus, and specific examples
include composites of Li, S, and P. If the ion-conductive material (C) contains phosphorus,
the weight ratio of phosphorus is preferably 0.15 to 0.55.
[0033] The use of such an ion-conductive material containing a specific amount of phosphorus
reduces resistance when sulfur, electrons, and lithium ions react with each other
at the reaction interface in the cathode mixture layer, thereby improving the charge/discharge
capacity of the all-solid-state lithium-sulfur battery. In contrast, if the weight
ratio of phosphorus in the ion-conductive material (C) is less than 0.15 or more than
0.55, a sufficient charge/discharge capacity cannot be ensured for an all-solid-state
lithium-sulfur battery including such a cathode mixture in some cases, depending on
the amperage during charge or discharge. In this regard, it is presumed that if the
weight ratio of phosphorus is more than 0.55, the interaction will occur so that phosphorus
excessively acts on sulfur and thus the effect of deactivating sulfur is increased,
resulting in reduced charge/discharge capacity.
[0034] The composite of Li, S, and P is preferably a composite obtained by mechanically
milling Li
2S, S, and P (hereafter, referred to simply as the composite of Li
2S, S, and P) or a composite obtained by mechanically milling Li
2S and P
xS
y where x and y independently represents an integer that gives a stoichiometric ratio
(hereafter, referred to simply as the composite of Li
2S and P
xS
y). This is because by mechanical milling, bonds can be easily rearranged and an amorphous
ion-conductive material can be obtained.
[0035] The term "composite" as used herein does not refer to a mere mixture of predetermined
components, but refers to a mixture of predetermined components to which a mechanical,
thermal, or chemical energy has been applied to cause part or all of the predetermined
components to undergo a chemical reaction. Moreover, the phrase "formed into a composite"
as used herein does not refer to merely mixing predetermined components, but refers
to mixing predetermined components followed by applying a mechanical, thermal, or
chemical energy to cause part or all of the predetermined components to undergo a
chemical reaction.
[0036] If the ion-conductive material is the composite of Li
2S, S, and P or the composite of Li
2S and P
xS
y, the molar ratio of Li
2S in each of the composites may be arbitrarily selected. Preferably, the molar ratio
of Li
2S is an amount such that the composite contains phosphorus at a weight ratio of 0.15
to 0.55.
[0037] The mechanical milling may be carried out by conventionally known methods. Specifically,
the mechanical milling may be carried out, for example, by using a planetary ball
mill at a rotation speed of 225 to 500 rpm and a revolution speed of 450 to 1000 rpm
(in the counter direction to the rotation) for 0.5 to 10 hours.
[0038] Whether Li
2S and P
xS
y have been formed into a composite or merely mixed can be determined by Raman spectroscopy.
For example, in the case of a composite of Li
2S and P
2S
5, a peak at 300 cm
-1 from P
2S
5 used as a starting material of the composite disappears or becomes small relative
to the main peak around 400 cm
-1. This indicates that Li
2S and P
2S
5 have been formed into a composite.
[0039] The composite of Li, S, and P may be obtained by mechanically milling at least one
selected from the group consisting of M
zS where M represents Si, Ge, B, or Al, and z represents an integer that gives a stoichiometric
ratio, phosphorus oxide, lithium oxide, and lithium iodide, together with Li
2S, S, and P or with Li
2S and P
xS
y. This is because the ion conductivity of the component (C) may be improved.
[0040] For the same reason, the composite of Li
2S and P
xS
y may further contain a lithium salt or a lithium nitride. The lithium slat is not
particularly limited, and examples include Li
3PO
4, Li
4SiO
4, and LiBH
4. The lithium nitride is also not particularly limited, and examples include Li
3N.
<Component (D): conductive material>
[0041] The cathode mixture of the present invention contains the conductive material (D)
as an electronic conductor. The conductive material (D) is not particularly limited,
and examples include acetylene black, activated charcoal, furnace black, carbon nanotube,
graphene, and carbon fiber. The component (D) may include only one type of conductive
component or two or more types of conductive components.
[0042] The component (D) preferably includes a conductive component (D1) that includes a
carbon material having a specific surface area of 1000 m
2/g or more. This is because the use of the conductive component having a specific
surface area of 1000 m
2/g or more increases the number of reaction points between the component (A) and the
component (D) and is thus suitable for providing an all-solid-state lithium-sulfur
battery having excellent charge/discharge capacity. The conductive component (D1)
more preferably has a specific surface area of 1800 m
2/g or more. The conductive component (D1) is preferably activated charcoal or a furnace
black having a hollow shell structure (Ketjen black (Lion Corporation)).
[0043] The term "specific surface area" as used herein refers to a BET specific surface
area determined by the Brenauer-Emmet-Telle (BET) method. Specifically, it is determined
using a nitrogen adsorption isotherm measured by adsorbing nitrogen gas onto a conductive
material sample at liquid nitrogen temperature. As an apparatus to determine the BET
specific surface area, for example, an automatic specific surface area/pore distribution
measuring apparatus (BELSORP-mini II, BEL Japan, Inc.) may be used.
[0044] The furnace black having a hollow shell structure refers to one type of conductive
furnace black that has a hollow shell structure with a porosity of about 60 to 80%.
The term "hollow shell structure" refers to a structure in which an outer shell in
particle form is formed by thinly assembled graphite crystals, and the inside of the
outer shell is hollow.
[0045] The conductive component (D1) is preferably in the shape of particles having an average
particle size of 0.2 to 200 µm. If the average particle size is less than 0.2 µm,
such a component may be difficult to handle because, for example, it can easily scatter.
Conversely, if the average particle size is more than 200 µm, such a component may
show poor dispersibility in the cathode mixture, resulting in reduced charge/discharge
capacity. The average particle size as used herein refers to a volume average particle
size measured by a laser diffraction method.
[0046] The component (D) may further include at least one conductive component (D2) selected
from the group consisting of graphite, acetylene black, carbon nanotube, and carbon
fiber, in addition to the conductive component (D1). This is because if the electric
conductivity of the conductive component (D1) is low, the further use of the conductive
component (D2) having a high electric conductivity improves electron conductivity
in the cathode mixture, which may result in further improved charge/discharge capacity.
[0047] In the case where the component (D) includes the conductive component (D2) together
with the conductive component (D1), the weight ratio thereof ((D1):(D2)) is preferably
9.5:0.5 to 5:5. This is because the reaction shown in the formula (1) can be more
promoted by increasing the proportion of the conductive component (D1) which has a
large specific surface area and can provide many reaction points with the component
(A).
[0048] In the cathode mixture of the present invention, the combined amount of the component
(A) and the component (B) (hereafter, also referred to as the total amount of the
components (A) and (B)) is preferably 40% by weight or more of the total cathode mixture.
If the total amount of the components (A) and (B) is less than 40% by weight of the
total cathode mixture, although a certain charge/discharge capacity (for example,
200 mAh/g or more per cathode mixture) can be ensured when low current flows, the
charge/discharge capacity may be insufficient when high current flows.
[0049] The total amount of the components (A) and (B) is preferably 65% by weight or less
of the total cathode mixture. If the total amount of the components (A) and (B) is
more than 65% by weight of the total cathode mixture, the proportion of the ion-conductive
material (C) and the conductive material (D) in the cathode mixture is reduced, possibly
resulting in a decrease in charge/discharge efficiency. The total amount of the components
(A) and (B) is more preferably 50 to 65% by weight of the total cathode mixture.
[0050] In the cathode mixture of the present invention, the ratio of the components, i.e.,
the ratio of the total amount of the components (A) and (B), the amount of the component
(C), and the amount of the component (D) (component (A)+component (B): component (C):
component (D)), by weight, is preferably 40-65:10-50:5-25. If the proportion of the
ion-conductive material (C) is smaller than the above range, the amount of lithium
ions that can move to the cathode is reduced, possibly resulting in an insufficient
charge/discharge capacity. Conversely, if the proportion is larger than the above
range, the proportion of the conductive material (D) in the cathode mixture is reduced,
possibly resulting in a lowered charge/discharge capacity per cathode mixture. Moreover,
if the proportion of the conductive material (D) is smaller than the above range,
the amount of electrons that can move to the cathode is reduced, possibly resulting
in an insufficient charge/discharge capacity. Conversely, if the proportion is larger
than the above range, the proportion of the ion-conductive material (C) in the cathode
mixture is reduced, possibly resulting in a lowered charge/discharge capacity per
cathode mixture.
[0051] The cathode mixture of the present invention is preferably obtained by mixing the
component (A) and the component (B) first and then mixing the resulting mixture with
the component (C) and the component (D). This is because in such a cathode mixture,
it is more ensured that the component (A) and the component (B) exist close to each
other, and therefore the electron donation from P of the component (B) to S of the
component (A) is more ensured.
[0052] The cathode mixture of the present invention may contain optional components such
as a binder or solvent, if necessary.
<Binder>
[0053] The binder is not particularly limited, and may be a thermoplastic resin, a thermosetting
resin, or the like. Examples include polyethylene, polypropylene, polytetrafluoroethylene
(PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene
copolymers, tetrafluoroethylene-hexafluoropropylene copolymers (FEP), tetrafluoroethylene-perfluoroalkyl
vinyl ether copolymers (PFA), vinylidene fluoride-hexafluoropropylene copolymers,
vinylidene fluoride-chlorotrifluoroethylene copolymers, ethylene-tetrafluoroethylene
copolymers (ETFE resins), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene
copolymers, propylene-tetrafluoroethylene copolymers, ethylene-chlorotrifluoroethylene
copolymers (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers,
vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymers, and
ethylene-acrylic acid copolymers. These binders may be used alone or in combinations
of two or more. Although the amount of the binder is not particularly limited, the
binder is preferably present in an amount of 0.01 to 10% by weight in the cathode
mixture.
<Solvent>
[0054] The solvent is not particularly limited, and examples include amine solvents such
as N,N-dimethylaminopropylamine and diethylenetriamine, ether solvents such as tetrahydrofuran,
ketone solvents such as methyl ethyl ketone, ester solvents such as methyl acetate,
amide solvents such as dimethylacetamide and 1-methyl-2-pyrrolidone, and hydrocarbon
solvents such as toluene, xylene, n-hexane, and cyclohexane. These solvents may be
used alone or in combinations of two or more. Although the amount of the solvent is
not particularly limited, the solvent is preferably present in an amount of 10 to
99% by weight in the cathode mixture. A cathode mixture layer can be easily prepared
from the cathode mixture containing the solvent. The solvent is removed by drying
in the preparation of a cathode mixture layer.
<Method for producing cathode mixture>
[0055] The cathode mixture of the present invention can be obtained by mixing the sulfur
and/or its discharge product (A), the elemental phosphorus and/or P
xS
y (B), the ion-conductive material (C), and the conductive material (D), and optional
components such as a binder or solvent, if necessary.
[0056] The method for producing the cathode mixture of the present invention is preferably
characterized by at least including:
step (1) of mixing the component (A) and the component (B); and
step (2) of mixing a mixture obtained in the step (1) with the component (C) and the
component (D) simultaneously or separately.
[0057] When the cathode mixture is prepared by mixing the components (A) and (B), which
serve as cathode active materials in the cathode mixture, first and then mixing the
resulting mixture with other components as described above, the component (A) and
the component (B) are located close to each other in the resulting cathode mixture,
and therefore electron donation from P of the component (B) to S of the component
(A) is allowed to proceed at a high probability. This electron donation significantly
improves the reactivity of the reaction shown in the formula (1). As a result, if
the cathode mixture is used in a cathode mixture layer of an all-solid-state lithium-sulfur
battery, the resulting all-solid-state lithium-sulfur battery shows low resistance
when sulfur, electrons, and lithium ions react with each other at the reaction interface,
and thus has excellent charge/discharge characteristics.
[0058] Thus, the present invention also encompasses a method for producing the cathode mixture
which characteristically includes the steps (1) and (2).
[0059] In the steps (1) and (2), the components may be mixed by any method, such as, for
example, by using Planetary Ball Mill (Fritsch), Hybridization System (Nara Machinery
Co., Ltd.), Cosmos (Kawasaki Heavy Industries, Ltd.), Mechano Fusion System (Hosokawa
Micron Corporation), Nobilta NOB (Hosokawa Micron Corporation), Mechanomill (Okada
Seiko Co., Ltd.), Thetacomposer (Tokuju Corporation), Nanosonic Mill (Inoue MFG.,
Inc.), Kneader (Inoue MFG., Inc.), Supermasscolloider (Masuko SangyoCo., Ltd.), nano-mech
REACTOR (Techno-eye), Konel Despa (Asada Iron Works Co., Ltd.), Planetary Mixer (Asada
Iron Works Co., Ltd.), Miracle KCK (Asada Iron Works Co., Ltd.), or the like. The
mixing conditions are not particularly limited, and may be at a rotation speed of
100 to 200 rpm and a revolution speed of 200 to 400 rpm (in the counter direction
to the rotation) for 0.5 to 10 hours.
[0060] In the step (2), when the mixture of the component (A) and the component (B) is mixed
with the other components (the component (C), the component (D), and other components),
the mixing order is not particularly limited. The mixture and the other components
may be mixed all at once, or alternatively, the component (C), the component (D),
and other components may be added to and mixed with the mixture separately from each
other at any timing.
[0061] In the method for producing the cathode mixture, the step (2) may be followed by
heat treatment. This is because heat treatment can increase the strength of the contact
interfaces of the components (A) to (D) in the cathode mixture and thus can reduce
the interfacial resistance. The heat treatment may be carried out in any manner, such
as, for example, at 80°C to 250°C, preferably 100°C to 200°C, for one second to 10
hours in an atmosphere of argon, nitrogen, air or the like. The heat treatment may
be carried out using conventionally known heating apparatuses. Specific examples include
constant temperature dryers, fan dryers, vacuum dryers, and infrared dryers.
«All-solid-state lithium-sulfur battery»
[0062] Next, the all-solid-state lithium-sulfur battery of the present invention will be
described with reference to drawings.
[0063] The all-solid-state lithium-sulfur battery includes a cathode mixture layer containing
the cathode mixture of the present invention, a solid electrolyte layer, an anode,
and a current collector.
[0064] The term "all-solid-state" as used herein refers to one that includes a polymeric
solid electrolyte and/or an inorganic solid electrolyte as the electrolyte, in which
the anode, the solid electrolyte layer, and the cathode mixture layer are substantially
free of solvents. The phrase "substantially free of solvents" as used herein means
that a trace amount of solvent may be left.
[0065] Fig. 1 is a cross-sectional view schematically showing an exemplary embodiment of
the all-solid-state lithium-sulfur battery of the present invention. As shown in Fig.
1, an all-solid-state lithium-sulfur battery 10 includes an anode 2, a solid electrolyte
layer 3, and a cathode mixture layer 4 that are laminated in this order, and also
includes current collectors (an anode current collector 1 and a cathode current collector
5) on its sides. The current collector (anode current collector, cathode current collector),
the anode, the solid electrolyte layer, and the cathode mixture layer are described
in this order below.
<Current collector>
[0066] The current collector is not particularly limited. For example, Al, Cu, Ni, stainless
steel and the like can be used. As the anode current collector, Cu is preferably used
because it is less likely to form an alloy with lithium and it can be easily processed
into a thin membrane. As the cathode current collector, Al is preferably used because
it can be easily processed into a thin membrane and it is low cost.
<Anode>
[0067] The anode is not particularly limited as long as it contains a material that absorbs
and releases lithium ions as an anode active material. Examples of the material that
absorbs and releases lithium ions include metallic lithium, lithium alloys, metal
oxides, metal sulfides, and carbonaceous materials that absorb and release lithium
ions. Examples of lithium alloys include alloys of lithium with aluminum, silicon,
tin, magnesium, indium, calcium, or the like. Examples of metal oxides include tin
oxides, silicon oxides, lithium titanium oxides, niobium oxides, and tungsten oxides.
Examples of metal sulfides include tin sulfides and titanium sulfides. Examples of
carbonaceous materials that absorb and release lithium ions include graphite, coke,
mesophase pitch carbon fibers, spherical carbon, and resin baked carbon.
[0068] The anode may be prepared by any method. Examples include a method in which the material
that absorbs and releases lithium ions is pressed and a method in which an anode precursor
dispersion containing the material that absorbs and releases lithium ions and a solvent
is applied to an anode current collector, dried and pressed. The solvent contained
in the anode precursor dispersion may be as described above for the cathode mixture.
The solvent is used to facilitate application of the anode precursor dispersion, and
is removed by drying after the application.
<Solid electrolyte layer>
[0069] The solid electrolyte layer may be formed of a polymeric solid electrolyte and/or
an inorganic solid electrolyte. The inorganic solid electrolyte may be a solid electrolyte
having an electric conductivity of 0.1 mS/cm or higher, for example. Although the
solid electrolyte is not particularly limited as long as it has an electric conductivity
of 0.1 mS/cm or higher, specific examples include lithium salts, lithium sulfides,
lithium oxides, and lithium nitrides.
[0070] The solid electrolyte is preferably a lithium salt, a lithium sulfide, or a combination
thereof, because of their high electric conductivity and low grain boundary resistance.
[0071] Examples of the lithium salt include, but are not limited to, LiBH
4 and LiI. Examples of the lithium sulfide include, but are not limited to, composites
with the P
xS
y described above, specifically, the composites of Li
2S and P
xS
y described above. Other examples include composites of Li
2S and P
xS
y and further GeS
2, SiS
2, Li
3PO
4, Li
4SiO
4, or the like. Examples of the lithium oxide include, but are not limited to, Li
2O and Li
2O
2. Examples of the lithium nitride include, but are not limited to, Li
3N. These solid electrolytes may be used alone or in combinations of two or more.
[0072] The solid electrolyte layer formed of the inorganic solid electrolyte may be prepared
by, for example, a method in which the solid electrolyte is press-formed or a method
in which the solid electrolyte is dispersed in a solvent and the dispersion is applied
and dried. The method in which the solid electrolyte is press-formed is not particularly
limited, and may be carried out for example by sandwiching and pressing the solid
electrolyte between an anode current collector and a cathode current collector, or
by pressing the solid electrolyte using a jig of a press. In the case where the solid
electrolyte layer is prepared by the method in which the solid electrolyte is dispersed
in a solvent and the dispersion is applied and dried, the dried solid electrolyte
layer may be pressed in the same manner as described above. The solvent used for dispersing
the solid electrolyte may be as described above for the cathode mixture. When the
solid electrolyte layer is prepared by these methods, heat treatment may be performed
at any timing in order to reduce the interfacial resistance of the solid electrolyte
layer and to improve the compactness thereof.
[0073] Examples of the solid electrolyte layer formed of the polymeric solid electrolyte
include polyethylene oxide polymers containing lithium salts such as lithium perchlorate
or lithium bis(trifluoromethanesulfonyl)amide.
<Cathode mixture layer>
[0074] The cathode mixture layer may be prepared by, for example, a method in which the
cathode mixture is supported on a cathode current collector or a method in which the
cathode mixture is press-formed. The method in which the cathode mixture is supported
on a cathode current collector is not particularly limited, and may be carried out
for example by press-forming the cathode mixture, or by making the cathode mixture
into a paste using an organic solvent or the like, applying the resulting cathode
mixture to a cathode current collector, drying and then fixing them to each other
by, for example, pressing. The method in which the cathode mixture is press-formed
is not particularly limited, and may be carried out for example by sandwiching and
pressing the cathode mixture between a solid electrolyte layer and a cathode current
collector, or by pressing the cathode mixture using a jig of a press. The cathode
mixture may be applied to a cathode current collector by any method, such as by slit
die coating, screen coating, curtain coating, knife coating, gravure coating, or electrostatic
spray coating. When the cathode mixture layer is prepared by these methods, heat treatment
may be performed at any timing in order to reduce the interfacial resistance of the
cathode mixture layer and to improve the compactness thereof.
[0075] The all-solid-state lithium-sulfur battery may include a separator and the like in
addition to the above-described anode current collector, anode, solid electrolyte
layer, cathode mixture layer, and cathode current collector. The all-solid-state lithium-sulfur
battery may have any shape, such as a coin, button, sheet, laminate, cylindrical,
flat, or rectangular shape.
<Method for preparing all-solid-state lithium-sulfur battery>
[0076] The all-solid-state lithium-sulfur battery may be prepared by any method such as
those described below.
[0077] First, a solid electrolyte is sandwiched and pressed between an anode current collector
and a cathode current collector to prepare a solid electrolyte layer. Next, a cathode
mixture is deposited on one side of the solid electrolyte layer and the stack is sandwiched
and pressed between the current collectors (the anode current collector on the solid
electrolyte layer side, and the cathode current collector on the cathode mixture side).
Thus, the cathode mixture layer and the cathode current collector are laminated on
one face of the solid electrolyte layer, while the anode current collector is laminated
on the other face of the solid electrolyte layer. Finally, after the anode current
collector is removed temporarily, an anode is put on the solid electrolyte layer on
the side opposite to the cathode mixture layer and then the anode current collector
is put on the anode side, followed by pressing. Thus, the anode and the anode current
collector are laminated on the other face of the solid electrolyte layer. Moreover,
the layers may be pressed one by one as described above, or two or more layers may
be deposited and pressed together to form a laminate. The all-solid-state lithium-sulfur
battery can be prepared by such methods.
<Application of all-solid-state lithium-sulfur battery>
[0078] The all-solid-state lithium-sulfur battery may be used in any application. For example,
the all-solid-state lithium-sulfur battery is suitable for electrical products that
require high energy density, such as hybrid cars and electric cars. The present invention
therefore can contribute to reducing CO
2 emissions.
EXAMPLES
[0079] The present invention is described with reference to examples below, but the present
invention is not limited to these examples.
1. Preparation of cathode active material (component
(A)/component (B))
(Cathode active material P(O))
[0080] Sulfur (Aldrich) was used as a cathode active material P(0).
(Cathode active material P(3))
[0081] Sulfur (Aldrich) and elemental phosphorus (Aldrich) were mixed at a weight ratio
of 97:3 using a planetary ball mill at a rotation speed of 185 rpm and a revolution
speed of 370 rpm (in the counter direction to the rotation) for 4 hours to give a
cathode active material P(3) which contained elemental phosphorus in an amount of
3% by weight of the amount of sulfur.
(Cathode active material P(5))
[0082] Sulfur (Aldrich) and elemental phosphorus (Aldrich) were mixed at a weight ratio
of 95:5 using a planetary ball mill at a rotation speed of 185 rpm and a revolution
speed of 370 rpm (in the counter direction to the rotation) for 4 hours to give a
cathode active material P(5) which contained elemental phosphorus in an amount of
5% by weight of the amount of sulfur.
(Cathode active material P(6))
[0083] Sulfur (Aldrich) and elemental phosphorus (Aldrich) were mixed at a weight ratio
of 94:6 using a planetary ball mill at a rotation speed of 185 rpm and a revolution
speed of 370 rpm (in the counter direction to the rotation) for 4 hours to give a
cathode active material P(6) which contained elemental phosphorus in an amount of
6% by weight of the amount of sulfur.
(Cathode active material P(8))
[0084] Sulfur (Aldrich) and elemental phosphorus (Aldrich) were mixed at a weight ratio
of 92:8 using a planetary ball mill at a rotation speed of 185 rpm and a revolution
speed of 370 rpm (in the counter direction to the rotation) for 4 hours to give a
cathode active material P(8) which contained elemental phosphorus in an amount of
8% by weight of the amount of sulfur.
(Cathode active material P(11))
[0085] Sulfur (Aldrich) and elemental phosphorus (Aldrich) were mixed at a weight ratio
of 89:11 using a planetary ball mill at a rotation speed of 185 rpm and a revolution
speed of 370 rpm (in the counter direction to the rotation) for 4 hours to give a
cathode active material P(11) which contained elemental phosphorus in an amount of
11% by weight of the amount of sulfur.
(Cathode active material P(14))
[0086] Sulfur (Aldrich) and elemental phosphorus (Aldrich) were mixed at a weight ratio
of 86:14 using a planetary ball mill at a rotation speed of 185 rpm and a revolution
speed of 370 rpm (in the counter direction to the rotation) for 4 hours to give a
cathode active material P(14) which contained elemental phosphorus in an amount of
14% by weight of the amount of sulfur.
(Cathode active material P(20))
[0087] Sulfur (Aldrich) and elemental phosphorus (Aldrich) were mixed at a weight ratio
of 80:20 using a planetary ball mill at a rotation speed of 185 rpm and a revolution
speed of 370 rpm (in the counter direction to the rotation) for 4 hours to give a
cathode active material P(20) which contained elemental phosphorus in an amount of
20% by weight of the amount of sulfur.
(Cathode active material PS(5))
[0088] Sulfur (Aldrich) and P
2S
5 (Aldrich) were mixed at a weight ratio of 95:5 using a planetary ball mill at a rotation
speed of 185 rpm and a revolution speed of 370 rpm (in the counter direction to the
rotation) for 4 hours to give a cathode active material PS (5) which contained P
2S
5 in an amount of 5% by weight of the amount of sulfur.
(Cathode active material PS(10))
[0089] Sulfur (Aldrich) and P
2S
5 (Aldrich) were mixed at a weight ratio of 90:10 using a planetary ball mill at a
rotation speed of 185 rpm and a revolution speed of 370 rpm (in the counter direction
to the rotation) for 4 hours to give a cathode active material PS (10) which contained
P
2S
5 in an amount of 10% by weight of the amount of sulfur.
(Cathode active material PS(20))
[0090] Sulfur (Aldrich) and P
2S
5 (Aldrich) were mixed at a weight ratio of 80:20 using a planetary ball mill at a
rotation speed of 185 rpm and a revolution speed of 370 rpm (in the counter direction
to the rotation) for 4 hours to give a cathode active material PS (20) which contained
P
2S
5 in an amount of 20% by weight of the amount of sulfur.
(Cathode active material PS(25))
[0091] Sulfur (Aldrich) and P
2S
5 (Aldrich) were mixed at a weight ratio of 75:25 using a planetary ball mill at a
rotation speed of 185 rpm and a revolution speed of 370 rpm (in the counter direction
to the rotation) for 4 hours to give a cathode active material PS (25) which contained
P
2S
5 in an amount of 25% by weight of the amount of sulfur.
(Cathode active material PS(33))
[0092] Sulfur (Aldrich) and P
2S
5 (Aldrich) were mixed at a weight ratio of 67:33 using a planetary ball mill at a
rotation speed of 185 rpm and a revolution speed of 370 rpm (in the counter direction
to the rotation) for 4 hours to give a cathode active material PS (33) which contained
P
2S
5 in an amount of 33% by weight of the amount of sulfur.
2. Preparation of ion-conductive material (component (C)) (Ion-conductive material
A)
[0093] Li
2S (Furuuchi Chemical Co.) and P
2S
5 (Aldrich) were weighed in a molar ratio of 80:20 and mixed in a mortar. The mixture
was treated in a planetary ball mill at a rotation speed of 250 rpm and a revolution
speed of 500 rpm (in the counter direction to the rotation) for 10 hours to give an
ion-conductive material A in which the weight ratio of phosphorus was 0.153. The obtained
ion-conductive material A had an electric conductivity of 0.4825 mS/cm.
[0094] The electric conductivity of ion-conductive materials was measured as follows.
[0095] A SUS304 cylindrical jig (10mm Φ), height 10 mm) (hereafter, also referred to as
current collector 2) was inserted into a polycarbonate cylindrical tube jig (inner
diameter 10 mm Φ, outer diameter 23 mm Φ, height 20 mm) from the bottom, 70 mg of
the ion-conductive material was put into the polycarbonate cylindrical tube jig from
the top, and then a SUS304 cylindrical jig (10mm Φ, height 15 mm) (hereafter, also
referred to as current collector 1) was inserted into the polycarbonate cylindrical
tube jig from the top to sandwich the ion-conductive material therebetween. The sandwiched
ion-conductive material was pressed at a pressure of 200 MPa for 3 minutes to form
an ion-conductive material layer having a diameter of 10 mm Φ and a thickness of about
0.5 mm. In this way, test samples for measuring electric conductivity were prepared.
The resistance of the test samples was determined by alternating current impedance
analysis with Cell Test System 1400 (Solartron), and the electric conductivity was
calculated using the thickness and diameter of the ion-conductive material layer (applied
voltage 50 mV, measurement frequency 1 to 1,000,000 Hz).
(Ion-conductive material B)
[0096] Li
2S and P
2S
5 were weighed in a molar ratio of 65:35 and mixed in a mortar. The mixture was treated
in a planetary ball mill at a rotation speed of 250 rpm and a revolution speed of
500 rpm (in the counter direction to the rotation) for 10 hours to give an ion-conductive
material B in which the weight ratio of phosphorus was 0.201. The obtained ion-conductive
material B had an electric conductivity of 0.0584 mS/cm.
(Ion-conductive material C)
[0097] Li
2S and P
2S
5 were weighed in a molar ratio of 60:40 and mixed in a mortar. The mixture was treated
in a planetary ball mill at a rotation speed of 250 rpm and a revolution speed of
500 rpm (in the counter direction to the rotation) for 10 hours to give an ion-conductive
material C in which the weight ratio of phosphorus was 0.213. The obtained ion-conductive
material C had an electric conductivity of 0.0209 mS/cm.
(Ion-conductive material D)
[0098] Li
2S and P
2S
5 were weighed in a molar ratio of 40:60 and mixed in a mortar. The mixture was treated
in a planetary ball mill at a rotation speed of 250 rpm and a revolution speed of
500 rpm (in the counter direction to the rotation) for 10 hours to give an ion-conductive
material D in which the weight ratio of phosphorus was 0.245. The obtained ion-conductive
material D had an electric conductivity of 0.0003 mS/cm.
(Ion-conductive material E)
[0099] Li
2S, red phosphorus, and sulfur were weighed in a molar ratio of 1.8:2:3.2 and mixed
in a mortar. The mixture was treated in a planetary ball mill at a rotation speed
of 250 rpm and a revolution speed of 500 rpm (in the counter direction to the rotation)
for 10 hours to give an ion-conductive material E in which the weight ratio of phosphorus
was 0.250. The obtained ion-conductive material E had an electric conductivity of
0.1644 mS/cm.
(Ion-conductive material F)
[0100] Li
2S, red phosphorus, and sulfur were weighed in a molar ratio of 1.8:2:2.2 and mixed
in a mortar. The mixture was treated in a planetary ball mill at a rotation speed
of 250 rpm and a revolution speed of 500 rpm (in the counter direction to the rotation)
for 10 hours to give an ion-conductive material F in which the weight ratio of phosphorus
was 0.288. The obtained ion-conductive material F had an electric conductivity of
0.0761 mS/cm.
(Ion-conductive material G)
[0101] Li
2S, red phosphorus, and sulfur were weighed in a molar ratio of 1.2:2:1.4 and mixed
in a mortar. The mixture was treated in a planetary ball mill at a rotation speed
of 250 rpm and a revolution speed of 500 rpm (in the counter direction to the rotation)
for 10 hours to give an ion-conductive material G in which the weight ratio of phosphorus
was 0.382. The obtained ion-conductive material G had an electric conductivity of
0.0333 mS/cm.
(Ion-conductive material H)
[0102] Li
2S, red phosphorus, and sulfur were weighed in a molar ratio of 0.8:2:1.4 and mixed
in a mortar. The mixture was treated in a planetary ball mill at a rotation speed
of 250 rpm and a revolution speed of 500 rpm (in the counter direction to the rotation)
for 10 hours to give an ion-conductive material H in which the weight ratio of phosphorus
was 0.431. The obtained ion-conductive material H had an electric conductivity of
0.0086 mS/cm.
3. Preparation of conductive material (component (D))
(Conductive material A)
[0103] Furnace black (Ketjen black EC600JD, Lion Corporation, specific surface area: 1200
m
2/g) was used as a conductive material A.
(Conductive material B)
[0104] Activated charcoal (Kansai Coke and Chemicals Company, Limited., specific surface
area: 3000 m
2/g) was used as a conductive material B.
(Conductive material C)
[0105] A mixture of 9 parts by weight of activated charcoal (Kansai Coke and Chemicals Company,
Limited., specific surface area: 3000 m
2/g) and 1 part by weight of furnace black (Ketjen black EC600JD, Lion Corporation,
specific surface area: 1200 m
2/g) was used as a conductive material C.
(Conductive material D)
[0106] A mixture of 9 parts by weight of activated charcoal (Kansai Coke and Chemicals Company,
Limited., specific surface area: 3000 m
2/g) and 1 part by weight of graphite (Wako Pure Chemical Industries, Ltd., specific
surface area: 5 m
2/g) was used as a conductive material D.
4. Preparation of cathode mixture
(Examples 1 to 3 and Comparative Example 1)
[0107] The cathode active material shown in Table 1 was used as the cathode active material
(component (A) +component (B)), the ion-conductive material A was used as the ion-conductive
material (component (C)), and the conductive material A was used as the conductive
material (component (D)). An amount of 100 mg of the cathode active material, 80 mg
of the ion-conductive material, and 20 mg of the conductive material were weighed
so that these components were present in a compositional ratio (weight ratio) of 50:40:10.
Using a planetary ball mill (premium line P-7, Frilsch, revolution radius: 0.07 m,
rotation radius: 0.0235 m, ratio of rotation to revolution: -2), these components
were then mixed in a 45 mL pot with 5 mm zirconia balls (about 40 g) at a revolution
speed of 370 rpm for 4 hours to prepare a cathode mixture for all-solid-state lithium-sulfur
batteries.
(Examples 4, 5)
[0108] The cathode active material shown in Table 1 was used as the cathode active material
(component (A) +component (B)), the ion-conductive material C was used as the ion-conductive
material (component (C)), and the conductive material A was used as the conductive
material (component (D)). An amount of 100 mg of the cathode active material, 80 mg
of the ion-conductive material, and 20 mg of the conductive material were weighed
so that these components were present in a compositional ratio (weight ratio) of 50:40:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Examples 6 to 9)
[0109] The cathode active material shown in Table 1 was used as the cathode active material
(component (A) +component (B)), the ion-conductive material D was used as the ion-conductive
material (component (C)), and the conductive material A was used as the conductive
material (component (D)). An amount of 100 mg of the cathode active material, 80 mg
of the ion-conductive material, and 20 mg of the conductive material were weighed
so that these components were present in a compositional ratio (weight ratio) of 50:
40: 10, and mixed under the same conditions as in Example 1 to prepare a cathode mixture
for all-solid-state lithium-sulfur batteries.
(Example 10)
[0110] The cathode active material PS (10) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material E was used as the ion-conductive material
(component (C)), and the conductive material A was used as the conductive material
(component (D)). An amount of 100 mg of the cathode active material, 80 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 50: 40: 10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Comparative Example 2)
[0111] The cathode active material P(0) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material A was used as the ion-conductive material
(component (C)), and the conductive material A was used as the conductive material
(component (D)). An amount of 120 mg of the cathode active material, 60 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 60:30:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Examples 11, 12)
[0112] The cathode active material shown in Table 1 was used as the cathode active material
(component (A) +component (B)), the ion-conductive material C was used as the ion-conductive
material (component (C)), and the conductive material A was used as the conductive
material (component (D)). An amount of 120 mg of the cathode active material, 60 mg
of the ion-conductive material, and 20 mg of the conductive material were weighed
so that these components were present in a compositional ratio (weight ratio) of 60:
30: 10, and mixed under the same conditions as in Example 1 to prepare a cathode mixture
for all-solid-state lithium-sulfur batteries.
(Examples 13 to 15)
[0113] The cathode active material shown in Table 1 was used as the cathode active material
(component (A) +component (B)), the ion-conductive material D was used as the ion-conductive
material (component (C)), and the conductive material A was used as the conductive
material (component (D)). An amount of 120 mg of the cathode active material, 60 mg
of the ion-conductive material, and 20 mg of the conductive material were weighed
so that these components were present in a compositional ratio (weight ratio) of 60:
30: 10, and mixed under the same conditions as in Example 1 to prepare a cathode mixture
for all-solid-state lithium-sulfur batteries.
(Example 16)
[0114] The cathode active material PS (5) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material F was used as the ion-conductive material
(component (C)), and the conductive material A was used as the conductive material
(component (D)). An amount of 120 mg of the cathode active material, 60 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 60:30:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Example 17)
[0115] The cathode active material PS (10) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material C was used as the ion-conductive material
(component (C)), and the conductive material A was used as the conductive material
(component (D)). An amount of 126 mg of the cathode active material, 54 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 63:27:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Example 18)
[0116] The cathode active material PS (5) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material F was used as the ion-conductive material
(component (C)), and the conductive material A was used as the conductive material
(component (D)). An amount of 126 mg of the cathode active material, 54 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 63:27:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Comparative Example 3)
[0117] The cathode active material P(0) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material A was used as the ion-conductive material
(component (C)), and the conductive material A was used as the conductive material
(component (D)). An amount of 130 mg of the cathode active material, 50 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 65:25:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Comparative Example 4)
[0118] The cathode active material P(0) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material A was used as the ion-conductive material
(component (C)), and the conductive material A was used as the conductive material
(component (D)). An amount of 140 mg of the cathode active material, 40 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 70:20:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Example 19)
[0119] The cathode active material P (5) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material C was used as the ion-conductive material
(component (C)), and the conductive material B was used as the conductive material
(component (D)). An amount of 80 mg of the cathode active material, 100 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 40:50:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Example 20)
[0120] The cathode active material PS (10) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material B was used as the ion-conductive material
(component (C)), and the conductive material B was used as the conductive material
(component (D)). An amount of 120 mg of the cathode active material, 60 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 60:30:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Examples 21 to 23)
[0121] The cathode active material shown in Table 1 was used as the cathode active material
(component (A) +component (B)), the ion-conductive material C was used as the ion-conductive
material (component (C)), and the conductive material B was used as the conductive
material (component (D)). An amount of 120 mg of the cathode active material, 60 mg
of the ion-conductive material, and 20 mg of the conductive material were weighed
so that these components were present in a compositional ratio (weight ratio) of 60:30:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Example 24)
[0122] The cathode active material P (5) was used as the cathode active material (component(A)+component
(B)), the ion-conductive material G was used as the ion-conductive material (component
(C)), and the conductive material B was used as the conductive material (component
(D)). An amount of 120 mg of the cathode active material, 60 mg of the ion-conductive
material, and 20 mg of the conductive material were weighed so that these components
were present in a compositional ratio (weight ratio) of 60:30:10, and mixed under
the same conditions as in Example 1 to prepare a cathode mixture for all-solid-state
lithium-sulfur batteries.
(Example 25)
[0123] The cathode active material PS (10) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material H was used as the ion-conductive material
(component (C)), and the conductive material B was used as the conductive material
(component (D)). An amount of 120 mg of the cathode active material, 60 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 60:30:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Example 26)
[0124] The cathode active material PS (10) was used as the cathode active material (component
(A)+component(B)), the ion-conductive material B was used as the ion-conductive material
(component (C)), and the conductive material B was used as the conductive material
(component (D)). An amount of 130 mg of the cathode active material, 50 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 65:25:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Example 27)
[0125] The cathode active material PS (10) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material B was used as the ion-conductive material
(component (C)), and the conductive material B was used as the conductive material
(component (D)). An amount of 140 mg of the cathode active material, 40 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 70:20:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Example 28)
[0126] The cathode active material PS (10) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material B was used as the ion-conductive material
(component (C)), and the conductive material C was used as the conductive material
(component (D)). An amount of 120 mg of the cathode active material, 60 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 60:30:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Example 29)
[0127] The cathode active material PS (10) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material B was used as the ion-conductive material
(component (C)), and the conductive material C was used as the conductive material
(component (D)). An amount of 130 mg of the cathode active material, 50 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 65:25:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Examples 30, 31)
[0128] The cathode active material shown in Table 1 was used as the cathode active material
(component (A) +component (B)), the ion-conductive material B was used as the ion-conductive
material (component (C)), and the conductive material D was used as the conductive
material (component (D)). An amount of 120 mg of the cathode active material, 60 mg
of the ion-conductive material, and 20 mg of the conductive material were weighed
so that these components were present in a compositional ratio (weight ratio) of 60:
30: 10, and mixed under the same conditions as in Example 1 to prepare a cathode mixture
for all-solid-state lithium-sulfur batteries.
(Example 32)
[0129] The cathode active material PS (10) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material C was used as the ion-conductive material
(component (C)), and the conductive material D was used as the conductive material
(component (D)). An amount of 120 mg of the cathode active material, 60 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 60:30:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
(Example 33)
[0130] The cathode active material PS (10) was used as the cathode active material (component
(A)+component (B)), the ion-conductive material C was used as the ion-conductive material
(component (C)), and the conductive material D was used as the conductive material
(component (D)). An amount of 130 mg of the cathode active material, 50 mg of the
ion-conductive material, and 20 mg of the conductive material were weighed so that
these components were present in a compositional ratio (weight ratio) of 65:25:10,
and mixed under the same conditions as in Example 1 to prepare a cathode mixture for
all-solid-state lithium-sulfur batteries.
5. Preparation of all-solid-state lithium-sulfur battery
[0131] A SUS 304 cylindrical jig (10 mm Φ, height 10 mm) as an anode current collector was
inserted into a polycarbonate cylindrical tube jig (inner diameter 10 mm Φ, outer
diameter 23 mm Φ, height 20 mm) from the bottom, 70 mg of a solid electrolyte (a composite
obtained by firing 5Li
2S-GeS
2-P
2S
5 at 510°C for 8 hours) was put into the polycarbonate cylindrical tube jig from the
top, and then a SUS304 cylindrical tube jig (10 mm Φ, height 15 mm) as a cathode current
collector was inserted into the polycarbonate cylindrical tube jig from the top to
sandwich the solid electrolyte therebetween. The sandwiched solid electrolyte was
pressed at a pressure of 200 MPa for 3 minutes to form a solid electrolyte layer having
a diameter of 10 mm Φ and a thickness of about 0.6 mm.
[0132] Next, after the SUS304 cylindrical jig (cathode current collector) inserted from
the top was pulled out temporarily, one of the cathode mixtures prepared in the examples
and the comparative examples in an amount corresponding to 3.75 mg of the cathode
active material was put on the solid electrolyte layer in the polycarbonate cylindrical
tube, and the SUS304 cylindrical jig (cathode current collector) was again inserted
from the top. Then, the cathode mixture was pressed at a pressure of 200 MPa for 3
minutes to form a cathode mixture layer having a diameter of 10 mm Φ and a thickness
of about 0.1 mm.
[0133] Next, after the SUS304 cylindrical jig (anode current collector) inserted from the
bottom was pulled out, a stack of a 0.25 mm-thick lithium sheet (Furuuchi Chemical
Co.) punched to a diameter of 8 mm Φ using a hollow punch and a 0.3 mm-thick indium
sheet (Furuuchi Chemical Co.) punched to a diameter of 9 mm Φ using a hollow punch
as an anode was put into the polycarbonate cylindrical tube jig from the bottom, and
the SUS304 cylindrical jig (anode current collector) was again inserted from the bottom.
Then, the stack was pressed at a pressure of 80 MPa for 3 minutes to form a lithium-indium
alloy anode. In this way, all-solid-state lithium-sulfur batteries in which an anode
current collector, a lithium-indium alloy anode, a solid electrolyte layer, a cathode
mixture layer, and a cathode current collector were laminated in this order from the
bottom were prepared.
6. Evaluation method
(Charge/discharge test)
[0134] The all-solid-state lithium-sulfur batteries prepared as above were charged to full
at a current density of 0.64 mA/cm
2 using a charge/discharge device (ACD-M01A, Aska Electronic Co., Ltd.), and then the
capacity per cathode mixture of each battery during discharge at a current density
of 6.4 mA/cm
2 was measured. Table 1 shows the results.
REFERENCE SIGNS LIST
[0135]
- 1.
- Anode current collector
- 2.
- Anode
- 3.
- Solid electrolyte layer
- 4.
- Cathode mixture layer
- 5.
- Cathode current collector
- 10.
- All-solid-state lithium-sulfur battery